1. Field of the Invention
The present invention relates to actuators that have ICs (integrated circuits) integrated with the actuators.
2. Description of the Related Art
Heretofore, various control units, e.g. control units of automobiles, are known in order to control various actuators, such as electric motors and solenoid valves. In general, a control unit of an automobile has a CPU. Therefore, in order to reliably and stably operate the CPU, the control unit is located at an appropriate place within the automobile, where the CPU may suffer from less external influence. For example, such a place may be chosen within a vehicle cabin to ensure a more narrow range of possible variations of temperature, a smaller vibration level, and less chance for immersion in water. In general however, the actuator is either directly mounted to the object to be actuated, e.g., an automobile engine and a transmission, or is located in the vicinity of such an object. Therefore, long electrical line(s) have been used for connecting the control unit to the actuator.
In addition, the known control units have a circuit that produces a drive current for directly driving the actuator. Such drive currents have been supplied to the actuator via the electrical line(s). However, a considerable loss of power has typically been caused due to the long electrical line(s).
In recent years, there have been proposed actuators containing circuits, e.g., ICs, for producing drive currents. The control unit only has to supply a control signal having a relatively small current to the actuator via the electrical line(s). These types of actuators are known as “actuators integrated with ICs.” Japanese Laid-Open Patent Publication No. 7-307435 teaches such an actuator.
In case of the actuator disclosed in the above publication, typically, a current flowing through the actuator is on the order of a few hundreds of mA. Therefore, the temperature produced by the actuator usually does not exceed a permissible temperature range for the IC. For this reason, the IC is positioned between a connector and a coil such that electrical lines connecting the connector, the IC, and the coil, have the shortest practical lengths.
Most recently however, new types of actuators requiring a current in the range of 2–3 A have been developed and used practically. These types of actuators may generate a large amount of heat. Therefore, in situations where these types of actuators have been used and the IC is positioned between a connector and a coil such that electrical lines connecting the connector, the IC, and the coil, have the shortest practical lengths, there is a possibility that the IC may be heated beyond a permissible temperature range.